1. Technical Field
This invention relates generally to communication systems and more particularly to Electrostatic Discharge Circuits used to protect Radio Frequency transceivers within such communication systems.
2. Related Art
Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Communication systems typically operate in accordance with one or more communication standards. For instance, wired communication systems may operate according to one or more versions of the Ethernet standard, the System Packet Interface (SPI) standard, or various other standards. Wireless communication systems may operate in accordance with one or more standards including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), and/or variations thereof.
Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, et cetera communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or channels (e.g., one of the plurality of radio frequency (RF) carriers of the wireless communication system) and communicate over that channel(s). For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via the public switch telephone network, via the Internet, and/or via some other wide area network.
For each wireless communication device to participate in wireless communications, it includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). Typically, the transceiver includes a data modulation stage (baseband processor) and an RF stage. The baseband processor converts between data and baseband signals in accordance with the particular wireless communication standard. The RF stage converts between baseband signals and RF signals. The RF stage may be a direct conversion transceiver that converts directly between baseband and RF or may include one or more intermediate frequency stages.
In some constructs, the RF stage is formed on a single semi conductive substrate die. In other constructs, the RF stage is formed in conjunction with a baseband processor on a single semi conductive substrate die. In either case, prior to packaging of the single semi conductive substrate die, signal pads of the RF stage are susceptible to Electro Static Discharge (ESD). ESD protection is essential for protection of the circuitry of the RF stage that is exposed by the signal pads. This ESD protection must minimally load the signal pads while providing excellent ESD protection. Meeting this combination of requirements is difficult. As processing dimensions become smaller, challenges in meeting these requirements becomes greater.
These ESD protection requirements are not limited to RF circuits, however. Any circuits that operate upon information signals and that have signal or tuning pads exposed on the semi conductive die have these same or similar requirements. With some of these circuits, a first group of circuit elements are formed on the semi conductive die while other circuit components are formed as external components, e.g., package components. It is also difficult to protect these types of circuits from ESD events prior to packaging. Thus, these types of circuits have significant ESD protection requirements.